Camborne winger Alex Ducker scored a hat-trick of tries for the Duchy, who had Albion full-back Matt Shepherd impressing for them.
Devon had led 10-7 at the break but Cornwall, coached by former Albion boss Graham Dawe, who was making his first return to Brickfields since 2016, scored two quick tries at the start of the second half to take a grip of the game.
Both counties were using the game to look at players for next month’s County Championship.
Ivybridge’s Charlie Briant, Billy Pinkus, Ben Watts, Ben King and Lewis Paterson, Plymstock Albion Oaks players Tim Coats and Aiden Taylor and OPMs’ Jake Neville featured for Devon, while Saltash’s Lewis Wells and Liskeard-Looe’s Oliver Aggis were part of a Cornwall squad that also featured Albion players Shepherd, Jon Dawe and Fraser Honey.
Former Albion back Tom Putt gave Devon the lead on nine minutes with a penalty, but Cornwall hit back with a try from close range by Camborne hooker Tommy Lee-Southworth on 24 minutes, which Shepherd converted.
But Devon responded and regained their lead 13 minutes later when a clever chip kick by Mitch Pinkus bounced perfectly for his former Ivybridge half-back partner Watts to gather and touch-down. Putt added the conversion to make it 10-7.
Cornwall did end the half on the attack but Devon defended well to keep them out.
Putt cut the gap to one point with a penalty on 44 minutes but straight from the restart Cornwall scored another when the dangerous Shepherd broke through Devon’s defence and unselfishly put in Ducker for another. Shepherd again converted from out-wide.
Ducker then completed a hat-trick in the 57th minute when he went over in the left corner and Shepherd continued his 100 per cent kicking record by putting over the conversion.
Devon continued to battle hard and they had a lot of pressure in the closing minutes but were unable to get a second try.
OPMs winger Neville came on 10 minutes into the second half to a big cheer from his club team-mates, who had gone to watch him.
Devon and Cornwall will meet again in the County Championships on May 18 at Brixham.